A conservative prefers a narrower scope of government for a couple of reasons.

First, conservatives believe that market forces (and not politics) are what make the best decisions for a country's economy. Conservatives believe that the government should keep out of people's economic decisions (but not their personal ones) because of this. They think, for example, that allowing people to decide what kind of cars they want gets you a better economy than having the government tell car companies that cars must get a certain gas mileage.

Second, conservatives generally distrust the government. They believe that the government is generally likely to try to tyrannize the people. Therefore, they believe that there should be as little government intervention as possible.